International Atomic Energy Agency Vienna
IAEA-TECDOC-1951
Protection against Exposure Due to Radon Indoors and Gamma Radiation from
Construction Materials — Methods of Prevention
and Mitigation
@
IAEA-TECDOC-1951
IAEA-TECDOC-1951
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PROTECTION AGAINST EXPOSURE DUE TO RADON INDOORS AND
GAMMA RADIATION FROM CONSTRUCTION MATERIALS —
METHODS OF PREVENTION
AND MITIGATION
AFGHANISTAN ALBANIA ALGERIA ANGOLA
ANTIGUA AND BARBUDA ARGENTINA
ARMENIA AUSTRALIA AUSTRIA AZERBAIJAN BAHAMAS BAHRAIN BANGLADESH BARBADOS BELARUS BELGIUM BELIZE BENIN
BOLIVIA, PLURINATIONAL STATE OF
BOSNIA AND HERZEGOVINA BOTSWANA
BRAZIL
BRUNEI DARUSSALAM BULGARIA
BURKINA FASO BURUNDI CAMBODIA CAMEROON CANADA
CENTRAL AFRICAN REPUBLIC CHADCHILE CHINA COLOMBIA COMOROS CONGO COSTA RICA CÔTE D’IVOIRE CROATIA CUBACYPRUS
CZECH REPUBLIC DEMOCRATIC REPUBLIC
OF THE CONGO DENMARK DJIBOUTI DOMINICA
DOMINICAN REPUBLIC ECUADOR
EGYPT EL SALVADOR ERITREA ESTONIA ESWATINI ETHIOPIA FIJIFINLAND FRANCE GABON
GEORGIA GERMANY GHANA GREECE GRENADA GUATEMALA GUYANA HAITI HOLY SEE HONDURAS HUNGARY ICELAND INDIA INDONESIA
IRAN, ISLAMIC REPUBLIC OF IRAQIRELAND
ISRAEL ITALY JAMAICA JAPAN JORDAN KAZAKHSTAN KENYA
KOREA, REPUBLIC OF KUWAIT
KYRGYZSTAN
LAO PEOPLE’S DEMOCRATIC REPUBLIC
LATVIA LEBANON LESOTHO LIBERIA LIBYA
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MARSHALL ISLANDS MAURITANIA
MAURITIUS MEXICO MONACO MONGOLIA MONTENEGRO MOROCCO MOZAMBIQUE MYANMAR NAMIBIA NEPAL
NETHERLANDS NEW ZEALAND NICARAGUA NIGER NIGERIA
NORTH MACEDONIA NORWAY
OMANPAKISTAN PALAU PANAMA
PAPUA NEW GUINEA PARAGUAY
PERUPHILIPPINES POLAND PORTUGAL QATAR
REPUBLIC OF MOLDOVA ROMANIA
RUSSIAN FEDERATION RWANDA
SAINT LUCIA
SAINT VINCENT AND THE GRENADINES SAN MARINO SAUDI ARABIA SENEGAL SERBIA SEYCHELLES SIERRA LEONE SINGAPORE SLOVAKIA SLOVENIA SOUTH AFRICA SPAIN
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OF TANZANIA
UNITED STATES OF AMERICA URUGUAY
UZBEKISTAN VANUATU
VENEZUELA, BOLIVARIAN REPUBLIC OF
VIET NAM YEMEN ZAMBIA ZIMBABWE The following States are Members of the International Atomic Energy Agency:
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IAEA-TECDOC-1951
PROTECTION AGAINST EXPOSURE DUE TO RADON INDOORS AND
GAMMA RADIATION FROM CONSTRUCTION MATERIALS —
METHODS OF PREVENTION
AND MITIGATION
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© IAEA, 2021 Printed by the IAEA in Austria
May 2021
IAEA Library Cataloguing in Publication Data Names: International Atomic Energy Agency.
Title: Protection against exposure due to radon indoors and gamma radiation from construction materials : methods of prevention and mitigation / International Atomic Energy Agency.
Description: Vienna : International Atomic Energy Agency, 2021. | Series: IAEA TECDOC series, ISSN 1011–4289 ; no. 1951 | Includes bibliographical references.
Identifiers: IAEAL 21-01397 | ISBN 978-92-0-105521-7 (paperback : alk. paper) | ISBN 978-92-0-105621-4 (pdf)
Subjects: LCSH: Radiation sources — Safety measures. | Radon — Safety measures. |
FOREWORD
Radon is a chemically inert, naturally occurring radioactive gas generated by the radioactive decay of 238U and 226Ra, which are present in rocks, soils and building and construction materials. It has no smell, colour or taste, and is detectable only with special measurement instruments. Some types of rock have higher than average uranium and radium contents. These include light-coloured volcanic rocks, granites and dark shales, as well as sedimentary rocks including karst limestone, sandstone, chalk and some clays that contain traces of these rocks.
Radon is transported from soil and rocks by convection and diffuses into the upper layers of soil and then into the atmosphere. Radon is drawn into buildings as a result of wind action and pressure differences induced by air densities (stack effect). Soil gas infiltration is recognized as the most important source of radon in dwellings and other buildings. Other sources of radon include building and construction materials and water extracted from wells, but they are of less importance. In some areas of the world, particularly in countries with certain geology and with long and cold winters, some houses can have very high levels of radon.
The United Nations Scientific Committee on the Effects of Atomic Radiation has observed that, for most people, radon is the largest source of radiation exposure throughout their lifetime. The World Health Organization has estimated that the proportion of lung cancers linked to radon lies between 3% and 14%, depending on the average radon concentration in the country and the method of calculation.
IAEA Safety Standards Series No. GSR Part 3, Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards, establishes requirements for the protection of the public against exposure due to radon indoors. Where activity concentrations of radon in buildings are of concern for public health, governments are to establish an action plan of coordinated actions to reduce activity concentrations of radon in existing and future buildings.
One element of the action plan would be to include in building codes appropriate preventive measures and corrective actions to prevent the entry of 222Rn.
This publication describes methods for reducing the entry of radon into dwellings and other buildings (i.e. preventive measures for new buildings and corrective actions for existing buildings). The publication provides examples (with graphics) of methods for reducing radon in buildings that can be used with different types of building foundation. It also provides advice on the investigation of the entry of radon into buildings and on the design and technical parameters of measures and actions for reducing radon entry, as well as examples of some design features that may adversely impact the long term effectiveness of these measures. The publication contains practical information on the types of measurement that need to be considered to demonstrate compliance with established national reference levels for exposure to radionuclides in building and construction materials and other construction materials.
The IAEA officer responsible for this publication was O. German of the Division of Radiation, Transport and Waste Safety.
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The IAEA has no responsibility for the persistence or accuracy of URLs for external or third party Internet web sites referred to in this
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CONTENTS
1. INTRODUCTION ... 1
1.1. BACKGROUND ... 1
1.2. OBJECTIVE ... 2
1.3. SCOPE ... 3
1.4. STRUCTURE ... 3
2. BUILDING FOUNDATIONS, VENTILATION AND CONSTRUCTION MATERIALS THAT RELEASE RADON ... 4
2.1. TYPES OF FOUNDATION ... 4
2.2. TYPES OF VENTILATION ... 8
2.3. TYPES OF MATERIAL THAT MAY EXHALE RADON ... 12
3. RADON MITIGATION STRATEGIES IN EXISTING BUILDINGS ... 13
3.1. DIAGNOSTICS AND INVESTIGATION ... 13
3.1.1. Data about the building ... 14
3.1.2. Diagnostic measurement ... 15
3.2. RADON MITIGATION SOLUTIONS ... 19
3.2.1. Depressurization of the soil ... 19
3.2.2. Pressurization ... 31
3.3 MITIGATION OF RADON EMITTING FROM CONSTRUCTION MATERIALS IN BUILDINGS ... 34
4. MITIGATION OF EXPOSURES FROM RADON RELEASED FROM THE WATER SUPPLY ... 35
5. RADON PREVENTION STRATEGIES IN NEW BUILDINGS ... 37
5.1. SEALING ... 37
5.2. MEMBRANES ... 37
5.3. ACTIVE AND PASSIVE DEPRESSURIZATION ... 37
6. EFFECTIVENESS ASSESSMENT ... 41
7. BUILDING AND CONSTRUCTION MATERIALS ... 43
7.1. PROBLEM IDENTIFICATION ... 43
7.2. MITIGATION OF EXPOSURES FROM RADIONUCLIDES IN BUILDING AND CONSTRUCTION MATERIALS ... 44
APPENDIX. PROPERTIES AND POSITIONING OF THE FAN ... 47
REFERENCES ... 49
CONTRIBUTORS TO DRAFTING AND REVIEW ... 53
1. INTRODUCTION 1.1. BACKGROUND
Radon-222, commonly called radon, is a radioactive gas generated by the radioactive decay of
238U and 226Ra, which are present in rocks, soils and construction materials. Radon is continuously released into outdoor air, where it is quickly reduced to harmless concentrations.
However, when it enters an enclosed space, it can sometimes build up to potentially hazardous concentrations.
For many people, radon represents the major contributor to their lifetime exposure due to radiation. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) in two comprehensive reports in 2000 and 2006 [1, 2] concluded that inhalation of radon and its decay products are established carcinogens for the lung (doses to other organs and tissues were at least an order of magnitude smaller than the doses to the lung).
The International Committee on Radiological Protection has reviewed the scientific evidence of health effects due to exposure due to radon in several publications and has made recommendation on the protective actions needed against indoor exposure to radon [3‒7].
In 2009, the World Health Organization (WHO) published the its Handbook on Indoor Radon [8]. The WHO review of the recent studies on indoor radon and lung cancer in Europe, North America and Asia found that they provide strong evidence that radon causes a substantial number of lung cancers in the general population. The WHO estimates that the proportion of lung cancers attributable to radon range from 3 to 14%, depending on the average radon concentration in the country concerned and the calculation method used. The WHO finds that radon is the first cause of lung cancer after smoking.
IAEA Safety Standards Series No. GSR Part 3, Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards [9], establishes requirements for protection of the public against exposure due to radon indoors. In particular, para. 5.20 of GSR Part 3 places the responsibility on national authorities to “ensure that an action plan is established comprising coordinated actions to reduce activity concentrations of radon in existing buildings and in future buildings” [9].
IAEA Safety Standards Series No. SSG-32, Protection of the Public against Exposure Indoors due to Radon and other Natural Sources of Radiation [10], provides guidance on the actions to be included in the radon action plan. These actions include the following:
(1) To establish an appropriate reference level for 222Rn for dwellings and other buildings with high occupancy factors for members of the public;
(2) To decide what other types of building with high occupancy factors for members of the public, such as kindergartens, schools and hospitals are included in the scope of the action plan for radon;
(3) To facilitate the measurement of 222Rn in dwellings and other buildings with high occupancy factors for members of the public;
(4) To identify 222Rn prone areas;
(5) To give priority to actions to reduce activity concentrations of 222Rn in those situations for which such action is likely to be most effective;
(6) To include in building codes appropriate preventive measures and corrective actions to prevent the ingress of 222Rn and to facilitate further actions wherever necessary;
(7) To implement measures to control and reduce exposure due to 222Rn, including determining the circumstance under which measures are to be mandatory or to be voluntary;
(8) To evaluate the success of the action plan.
This TECDOC provides examples of possible preventive measures and corrective actions that could be considered by national authorities for including in national building codes, i.e. relating to item (6) in this list of elements of a radon action plan.
Paragraph 5.7 of GSR Part 3 requires that the regulatory body or other national authority ensures that the “remedial actions or protective actions are expected to yield sufficient benefits to outweigh the detriments associated with taking them, including detriments in the form of radiation risks” [9], i.e. that the remedial actions and protective actions are justified. This TECDOC provides examples of preventive measures and corrective actions that have been used successfully in some States. It is up to the national authorities to ensure that such examples are justified for use in their State.
Recommendations on limiting exposure and implementing radon preventive and mitigation measures are also expressed in the WHO’s publication on radon [8].
Building practices have an impact on radon concentrations. In areas where higher radon concentrations are a known risk, preventive building practices may be adopted to lower radon ingress into new structures. In buildings and homes that have elevated radon concentrations corrective or remedial actions need to be taken to reduce those concentrations. These remedial actions have been shown to be effective in lowering radon concentrations.
Since publication of GSR Part 3 in 2014, the IAEA has received many requests for advice and assistance in providing a comprehensive overview of mitigation techniques for lowering radon concentrations in buildings as well as techniques for reducing exposure from construction materials. In addition, guidance related to including preventive measures in building codes, has been requested.
Requirement 51 of GSR Part 3 requires that the exposure due to radionuclides in commodities, such as construction materials, will not contribute to annual effective doses to the population higher than 1 mSv [9]. This requirement is used for the justification of remedial actions needed to reduce exposure of the population in existing as well as newly build buildings. SSG-32 [10]
provides guidance on protection of the public against exposure to gamma rays from radionuclides in construction materials. This TECDOC provides practical advice on the measurements that can be performed to demonstrate compliance of the materials with the requirements of GSR Part 3 and practical advice on remedial actions against ionising radiation in construction materials.
1.2. OBJECTIVE
The main objective of this TECDOC is to provide a review of technical solutions for both corrective actions and preventive measures to reduce the ingress of radon indoors. This review includes the description of methods, design and implementation of measures and actions to reduce ingress of radon into buildings, and of the materials and equipment used in these solutions. The TECDOC also includes methods for measuring gamma radiation from radionuclides in building and construction materials and for reducing exposure due to gamma radiation from building and construction materials.
This TECDOC is aimed primarily at national authorities responsible for the development of national building codes; at national authorities responsible for the development and implementation of national radon action plans; and at building professionals responsible for the implementation of national building codes (e.g. architects, construction engineers). This TECDOC is also aimed at building and construction professionals designing and installing radon reducing measures, and measures for reducing exposure from building and construction
materials, as well as educational establishments providing higher education, including practical training, in construction and architecture.
1.3. SCOPE
The publication covers both mitigation measures for existing buildings and protective measures for new buildings. Detailed discussion is given on diagnosing the problem for a range of common construction and ventilation types and their influence on radon ingress into a building.
A comprehensive selection of mitigation methods and protective measures for new buildings are described. There is no single method that can be used in all cases. Some dwellings may need a combination of more than one method so that the radon levels are reduced to below the national reference level.
This TECDOC does not cover the following topics: the national system of regulatory control of indoor radon which is covered in SSG-32 [10] and in the Draft Safety Guide Protection of Workers against Exposure Due to Radon [11]; the regulatory control of building and construction materials which is described in Ref. [12]; the design and implementation of national and regional surveys of indoor radon or thoron which is covered in Ref. [13]; and the design and implementation of a national action plan to reduce public exposure due to radon indoors, which is covered in SSG-32 [10].
1.4. STRUCTURE
This TECDOC consists of seven Sections. Section 1 provides introduction to the publication.
Section 2 gives overview of basic knowledge on radon and construction properties that are necessary to be considered for designing any radon corrective or preventive action. In Section 3 mitigation methods for existing buildings are described while Section 4 deals with mitigation of radon when the source of radon in the household water. Radon preventive methods for new constructions are provided in Section 5. General considerations of efficiency assessment of preventive and corrective measures are provided in Section 6. Section 7 deals with the protection against gamma radiation arising from building and construction materials. The Appendix provides advice on the selection and installation of fans as part of the measures to reduce radon levels in buildings.
2. BUILDING FOUNDATIONS, VENTILATION AND CONSTRUCTION MATERIALS THAT RELEASE RADON
2.1. TYPES OF FOUNDATION
A building is generally constructed with one of four foundation types: (1) slab-on-grade, (2) crawl space, (3) basement with footings, or (4) basement1 with load bearing slab and wall construction [14]. Most buildings will use only one foundation type, while some, particularly where building extensions have been added over the years, may use several foundation types.
It is important to identify each foundation type to properly address radon prevention and mitigation issues in a building. All buildings will have some contact with the ground so they may potentially have a radon problem. Therefore, each foundation type can contribute to the radon concentration in the building. Radon reduction measures applied to a building may fail if the floors and walls forming the foundations are overlooked or ignored during the mitigation process.
The types of foundation are more or less the same around the world, although there may be some minor modifications.
Slab-on-grade is a type of foundation where the lowest floor of the building is a concrete slab poured directly on the ground at the existing grade level. Because the slab is in direct contact with the ground, a building built with this type of foundation may have a radon problem if the slab is cracked or it is punctured for the provision of services. A schematic drawing of a slab- on-grade type of foundation is shown in Fig. 1.
FIG. 1. Slab on grade type of foundation.
There are two sub-types of slab-on-grade foundation:
(a) The superstructure and/or walls built-off the floor slab;
(b) The superstructure and/or walls built-off strip or pad foundations, with the slab poured after the foundation walls have been installed.
Basement is a type of floor construction where the lowest floor of the building is a slab that is below grade level and has all or some of its walls in contact with the adjacent ground or bedrock [15]. There are various types of basement, for example:
(a) Full basement – where the basement is located beneath the full footprint of the building, and all of the external walls below grade level are in contact with the adjacent ground;
(b) Partial basement – where the basement is only located beneath part of the building;
(c) Semi-basement – where the building is cut into the hillside and some external walls are partially or fully below grade level in contact with the adjacent ground; and
(d) Stepped construction – where a building is stepped up a sloping site.
Whilst basements are typically a single storey below ground level of a building, they can also be multi-storey below ground level. An occupied space below ground level is referred to as a basement, whereas an unoccupied space below ground is usually referred to as a cellar.
A schematic drawing of these four types of basement or cellar are shown in Fig. 2.
From a radon protection point of view, methods for reducing radon are implemented in basements rather than cellars, as basements are occupied by people. The radon mitigation expert may also need to understand if and how radon moves from a cellar into the occupied areas of the building. It may be necessary to seal the cellar to prevent movement of radon from cellar into the occupied areas of the building. Cellars may also prove useful for locating mitigation ventilation fans and routing pipe work out of sight.
Basements can be found in all climates, and ground conditions. As basements have a larger surface area in contact with the ground (both floors and walls), and proximity to preferential pathways for the movement of radon under and around the foundation (e.g. utilities, floor-wall joints, sump pits), buildings with basements are more likely to have significant radon entry than for buildings with other foundation types.
There are two types of foundation used for buildings with basements: basement with footings and basement with load bearing slabs.
Basement with footings. In this construction type, the house is built on footings with the floors poured between the basement walls. The basement walls and floor are not created at the same time.
A schematic drawing of a basement with footings is presented in Fig. 3.
Basement with load bearing slab. In this construction type, the house is built on a solid load bearing slab. This allows for fewer radon entry points. The basement walls and floors are created at the same time.
A schematic drawing of a basement with load bearing slab is presented in Fig. 4.
FIG. 2. Different kinds of cellars and basements (reproduced with permission of IHS Markit from Ref. [15]).
FIG. 3. Basement with footings.
FIG. 4. Basement with load bearing slab.
Crawl space is a type of foundation with an open area beneath the lowest occupied space of the building. The lowest living or occupied level is built above the crawl space and is usually elevated 200 mm or so above grade. While crawl spaces are not habitable areas, they may contain utilities or mechanical ductwork that serves the rest of the building. Crawl spaces are often uncovered earthen material that can be a source of radon. If left untreated, they can contribute to elevated radon levels in the building. Some crawl spaces may have a poured concrete floor. When constructed, the crawl space needs to be provided with under floor vents to ensure ventilation under the floor to remove moisture that rises from the ground and to prevent timber rot in timber floors.
A schematic drawing of a crawl space type of foundation is presented in Fig. 5.
FIG. 5. Crawl space type of foundation.
2.2. TYPES OF VENTILATION
There are three common types of ventilation system used to ventilate dwellings: (a) natural draught ventilation; (b) mechanical exhaust air ventilation system; and (c) mechanical supply and exhaust air ventilation system having different influence on indoor radon accumulation or ventilation.
Natural draught ventilation.
Historically this is the method most commonly used across the world. It is based on pressure difference between the inside and the outside of the building which is induced by the difference in density between the indoor and outdoor air. The rate of air change is determined by the pressure flow (often referred to as the “stack or chimney effect” or “warm air rising effect”) induced by the pressure differences between the indoor and outdoor air, and the volume of the building.
A schematic drawing of a dwelling with natural draft ventilation is presented in Fig. 6.
The air exchange rate, also known as air change per hour (ACH), is defined as the ratio of airflow and the total volume of air given by Eq. (1):
ACH = ∆V/∆t ‧ 1/V (1)
where
∆V = Volume of air (in m3) exhausted in one hour;
∆t = Time = 1 hour;
V = Volume of the building (in m3).
The rate of air change is affected and determined by the number of indoor and outdoor air openings, e.g. passive ventilators, windows, doors, and their opening area. The rate of air change is also dependant on the airtightness of the building and is also influenced by the wind.
The draught system can provide reasonably stable ventilation on a yearly basis but is prone to have high daily variations.
The natural draught ventilation system works better in cold climates than warmer ones due to higher temperature differences between the inside and the outside of the building.
If a building which relies on natural ventilation has an elevated level of radon, it is usually not possible to reduce the radon levels to a specified level (e.g. below reference level) by natural ventilation alone. Instead, a far higher air exchange rate would be needed to solve an existing radon problem in the building.
FIG. 6. Natural draft ventilation.
Mechanical exhaust air ventilation system
In this system the rate of air change is determined by the fan rating in the mechanical exhaust, the area of the ventilation opening to the outside, and the airtightness of the building. Compared
to natural draught ventilation, this system is significantly less affected by the density difference between indoor and outdoor air and the influence of wind.
For dwellings with an installed mechanical exhaust air ventilation system, that have elevated radon levels originating from the soil, it is essential to find and seal all cracks and leaks in the floor construction and if needed also install a soil depressurization solution. Mechanical extraction of air from the building results in the air in the building being under pressurized compared to the external air, and also compared to the soil gases that contain radon. The pressure difference between the soil and the inside of the building draws the soil gases towards the inside of the building. The ventilation system will need to be carefully balanced to ensure that the system does not increase the radon problem from the ground.
If the elevated radon levels in the dwelling is caused by the exhalation of radon from the building and construction material, the solution can include installing a mechanical exhaust air ventilation system. However secondary effects need to be considered as well – increased ventilation without heat recovery may increase heat losses, which may be unacceptable in cold climates.
A schematic drawing of a dwelling with mechanical exhaust air ventilation system is presented in Fig. 7.
FIG. 7. Mechanical exhaust air ventilation system.
Mechanical supply and exhaust air ventilation system
In this system the rate of air change is determined by the balance between air supply and exhaust airflow rates. This is known in some areas of the world as an air-to-air exchanger or a heat recovery ventilator.
Compared to the natural draft ventilations and mechanical exhaust air ventilation systems, the mechanical supply and exhaust air ventilation system has a better ability to control and balance the movement of air through the building. Control can be applied to fans and ventilation grilles used for both incoming and exhaust air. A well-balanced system will result in far less influence
on the ventilation of the building from the weather, such as external air temperature and wind.
An unbalanced system may induce ingress of radon from the soil into the building and lead to elevated radon levels.
Mechanical supply and exhaust air ventilation would normally have enough capacity to solve an existing radon problem due to exhalation of radon from building and construction materials used in a building. However, systems that are designed for a high degree of energy efficiency may not have sufficient spare capacity to allow for increased airflows that may be necessary to reduce indoor radon levels.
A schematic drawing of a dwelling with a Mechanical supply and exhaust air ventilation system is presented in Fig. 8.
FIG. 8. Mechanical supply and exhaust air ventilation system.
With an existing mechanical supply and exhaust air ventilation system in a building and the elevated radon levels in the building coming from the soil air, it may be enough to adjust the system with a slight over pressure in the building to reduce the ingress of radon into the building and therefore lower the radon levels. However, in countries with very cold climates, care needs to be taken to prevent internal moist air entering into a layer in the interstitial structure of the building that is at dew point temperature, as it may condense and could freeze. As a consequence, it is important to consider the local building construction methods and the climate that they were built for when considering over-pressurizing a building. Furthermore, for larger multi-zone buildings, it may be difficult to control and balance airflows. It also involves greater cost with electrically controllable exhaust and inlet vents and the need for a sophisticated building management system. Therefore, such systems may be appropriate for individual houses but not for larger buildings.
Even with mechanical supply and exhaust air ventilation, it is still important to find and seal all significant cracks and leaks in the floor construction when implementing radon remedial
measures. If changes are not to be made to the ventilation system, then an active soil depressurization system will need to be installed to solve an existing radon issue.
2.3. TYPES OF MATERIAL THAT MAY EXHALE RADON
For the purposes of this publication, and in accordance with SSG-32 [10], ‘building materials’
are construction materials that are used for the construction of buildings such as dwellings, and offices, industrial premises and other workplaces. To provide a constancy with the terminology of the GSR Part 3 [9], dealing with commodities such as construction materials, this TECDOC uses both “building and construction materials”. Given that all stone-based construction materials are naturally occurring and mined from the earth, they contain trace amounts of uranium and radium. Therefore, it is mainly concrete construction material used for floors, walls or ceilings of buildings, or crashed stones used for filling beneath the buildings, that may emanate radon that contributes to the indoor radon concentrations.
Generally, concrete is made of roughly 10% cement, 10% water and 80% of aggregates of different fractions [16].
Models have been developed for the dose assessment of gamma radiation emitted from construction materials. These models use a reference room that is assumed to have the dimensions 3 m x 4 m x 2.5 m and that is made from concrete [17].
The level of radon in the room can be calculated using Eq. (2) (see Ref. [18]):
𝐶 = ( ). . ∑ 𝐸 . 𝐴 (2)
where
Cbm = Radon contribution to indoor air concentration from construction material 𝜆 = Radon decay constant = 0.00755
n = Air exchange rate = 0.5 volumes/hour V = Room or buildings inner volume = 30 m3 Ei = Radon exhalation rate = 13 Bq/m2h
Ai = Surface area of walls made using the construction material in the room = 55.4 m2 The radon exhalation from concrete is assumed to be 13 Bq/m2h for this exercise, which is also typical for untreated concrete surfaces, for building and construction materials with an activity concentration of about 60 Bq/kg Ra in accordance with [18].
The contribution of the construction material to the radon concentration in the room can be calculated using Eq. (2) above:
Cbm = (1/((0.00755 + 0.5) * 30)) * (13 * 55.4) = 50 Bq/m3
i.e. the construction material contributes about 50 Bq/m3 to the indoor radon concentration from the concrete alone, assuming the ventilation rate is 0.5 air change per hour, which is a typical exchange rate for some workplaces and dwellings.
For workplaces and municipal buildings, the airflow demands are typically higher, up to 1.0 air change per hour. This additional ventilation may reduce the above contribution from the construction material to the total indoor radon concentration to approximately 25 Bq/m3 for the same volume facility.
Knowing the contribution of building and construction materials to indoor radon concentrations is important in areas of the world with more stringent building codes. Some sustainable building standards necessitate very low radon concentrations in newly constructed buildings. If radon concentrations from building and construction materials are not accounted for, the lowest achievable radon concentration in the building may be higher than what is stipulated in these building codes without taking drastic additional protection measures. In addition, it is important that the building designer has a knowledge of the radium content of the building and construction materials, and for the constructor and the concrete producers to be able to control the uranium and radium contents of the aggregate (ballast) used in the concrete for such buildings.
3. RADON MITIGATION STRATEGIES IN EXISTING BUILDINGS
Generally, there are three approaches to radon mitigation: depressurisation of the ground beneath the building, over-pressurisation inside the building or in the ground beneath the building, and isolation. The approaches are explained later in the Section.
The key point in successful mitigation is proper execution of the mitigation methods, that are implemented by experts who are trained and have expert knowledge on the methods to reduce radon levels in buildings. This TECDOC does not provide exact solutions for every possible case therefore understanding of the principles is equally important as the guidance itself.
Prior to designing and installing the measures to reduce ingress of radon into the building, the expert will need to review the measurements that have been made of the radon levels in the building, request or carry out diagnostic tests to determine entry points for radon into the building, and make an assessment of the type of foundation and the construction pf the building to determine the most appropriate mitigation methods to be installed in the building.
3.1. DIAGNOSTICS AND INVESTIGATION
The first step in mitigating a radon problem is to review the measurement results for existing indoor radon level for the building. The report containing measurement results will include the measured radon levels, the measurement technique which needs to have been a long-term measurement, and the time period for the measurements. The measured radon levels need to be compared with the national reference level. All of this is important as the radon level will help to determine the most appropriate mitigation method for the building. Some mitigation methods are best applied to lower radon levels, i.e. radon levels which are slightly above the reference level, whereas other methods, or a combination of methods, can deal with a range of radon levels. If the radon level exceeds the national reference level, mitigation works needs to be carried out, and on completion, the radon levels in the building need to be measured to demonstrate that the mitigation methods used were successful.
There are a range of different methods of radon measurements. The most commonly used method are etched track detectors (solid state nuclear track detectors) that allow for a measurement period up to one year. As radon levels in a building vary with weather conditions and occupant use of the building, longer duration monitoring is needed to give a more accurate average radon level for the building. The measurement period is preferably from two months to twelve months. Where shorter measurement periods are used, they need to cover the heating season. Active measurement using integral electronic devices can also be used but their cost is in principle higher compared to passive devices. Even in this case, it is recommended that the period of measurement is not shorter than two months during the heating season, to allow for averaging of prevailing conditions [10].
Radon concentrations in buildings vary over time. The concentration depends on numerous factors, such as the availability of radon gas in ground (or water), air pressure conditions, time dependent permeability for radon gas of topsoil layers, building construction foundations and ventilation, air pressure conditions inside the building and use of the building.
When designing the measures for radon mitigation in existing buildings, all aspects influencing the radon levels need to be addressed. At the start of the mitigation, detailed data on radon entry routes into the buildings needs to be determined. Also, data on the building itself (such as construction materials used, type of foundation, layers beneath the visible ground floor, shafts) is often not known or is not reliable. Understanding these data is very important since it strongly affects the selection and success of the mitigation strategy starting from the concept, design, and details of execution.
Valuable sources of the information are the technical drawings (so called ‘blueprints’) for the building, if available. However, information found on the blueprints need to be verified to a sufficient extent to be deemed as reliable. In particular, this is valid for old buildings that have been reconstructed after the building was erected and the blueprints fail to capture most recent renovations. The same warning applies in the cases where changes to the blueprint might have not been recorded properly during the construction phase and the construction logs are not available. In practice, often information obtained with interviewing local community members can reveal potential discrepancies between the blueprints and the final building, e.g. material used under the floor during construction.
3.1.1. Data about the building
Before designing the radon mitigation measures, data on the building need to be collected in a systematic manner. It is recommended that a general drawing of the building represents the basis for recording the data.
The data have to comprise the following (the list is not exhaustive):
(a) General information on location of the building, with details about temperature range and expected wind conditions throughout the year and local ground characteristics, for example general permeability of the ground (different components will have different permeability that may also depend on moisture content e.g. clay, loam soil, sand, gravel) and other materials under the building, and information on air pressure from the ground, if available and/or relevant.
(b) General description of the building: terrain (flat or slope), how the building is following the terrain (e.g. flat, cascading or semi-buried), the use of the building, general footprint shape (e.g. rectangular, “L” shaped, “H” shaped) and approximate height of the building.
(c) Description of floors in the building, number of underground floors, if any, total estimated footprint area. This data is important for the estimation of natural pressure conditions in the building.
(d) Description of the building’s load bearing structure (e.g. concrete, wood, masonry), description of depth of foundation walls in the ground, and a description of the material used for the foundation walls.
(e) Definition of internal floor footprint areas within foundation walls. Estimation of shape and size of such area. Description of the expected underlaying layers, in particular identification of the air permeable layer. The preferential pathways due to settling of fill material and utility installation that occur in or under the floor structure, play an important role in establishing the radon mitigation approach.
(f) Description of sealing of the floor structure to the internal and external walls. The gap width between floor and internal/external walls, and materials of the floor and walls need to be noted. These parameters are important to plan for sealing of the gaps with an appropriate sealing technique. This sealing is often not present when initially inspecting the building.
(g) Year (or period) of construction of building and possible renovations or extensions to the original building; this data can often provide insight of typical construction practice of a given period. Often certain events like earthquakes or major floods may cause significant changes in building codes or practices affecting the ingress of radon into buildings.
(h) Estimated or measured airtightness of the building and description of windows and external doors. If the building is planned to be retrofitted to meet a specific energy standard, the airtightness of the building might be significantly altered. This can drastically affect the radon activity concentrations in the building.
(i) Location of the tunnels for utilities beneath the building, if present, and whether tunnels are closed at their ends, and if the tunnels are made of continuous material or made of modular elements with joints between the elements. Sometimes the tunnels are open at the pipe entry point in the boiler room.
(j) Location of the sewage pipes, including identification of sinks, floor sinks and other elements intended to collect wastewater. Location of any piping from the ground penetrating through the floor to the inside of the building.
(k) Location of the air exhaust or air supply vents, if any, and identification of the ducting and the point where internal air is released to the outside.
3.1.2. Diagnostic measurement
To properly design radon mitigation measures, additional information and measurements might be needed to understand the entry points of radon into building, and the volume of soil air entering the building.
Radon Entry points
Since no building is totally sealed from the ground, the common weak spots are presented for each of the following types of foundation:
(a) Concrete slab foundation;
(b) Basement;
(c) Crawl space.
A schematic drawing showing possible radon entry points into a dwelling is presented in Fig. 9.
FIG. 9. Radon entry points (reproduced with permission of IHS Markit from Ref. [19]).
Concrete slab foundation
Most concrete shrinks when hardening, and the shrinkage creates gaps that become leakage points for soil air containing radon. The leakage points are:
(a) All floor connections against the wall construction when the slab is poured to the wall.
This is also known as the floor-to-wall joint;
(b) All pipe and electrical installation penetrations through the concrete slab foundation;
(c) All floor slab against the pre-cast L-support. L-supports are mainly used as prebuilt die cast for the floating floor concrete and is a spot of radon leakage when the concrete hardens.
Basement
Basement with weight bearing footings and the concrete floor is cast afterwards are the weakest construction type against spots for soil radon entry. This is due to the concretes shrinking effect during its hardening. The house has many meters of this in each room of the basement:
(a) All floor connections against the wall construction when the slab is poured to the wall.
This is also known as the floor to wall joint.
(b) All pipe and electrical installations through the concrete slab foundation.
(c) All floor slab against the pre-cast L-support.
Basement house with slab-on-grade construction (a) All wall connections to the slab-on-grade floor;
(b) All pipe and electrical installation penetrations through the concrete slab foundation;
(c) All pipe and electrical installation penetrations through the concrete walls.
Crawl space
(a) All pipe and electrical installation penetrations through the floor construction.
Detection of radon entry points
The more important radon entry routes can normally be identified with a visual survey of the building. To help identify radon entry routes, an integrated radon measuring instrument with
“sniffing” capability function can be used. However, the interpretation of results can prove difficult if individual areas of the building cannot be isolated. Radon measurements by sniffer detectors will be affected by the weather on the day of the survey and if the building has been or has not been closed over the previous 24 hours. The protocols in some countries necessitate that the building be closed for 24 hours prior to such measurements, while the protocols in other countries do not. Once a radon professional gains experience with visual surveys of buildings, and increase their understanding of building construction techniques, they need to rely less on the use of a radon sniffer detector.
Air intake, air exhaust, air pressure measurement
To measure the air intake rate and the air exhaust rate is essential to establish if the building is under-pressurized or over-pressurized. One way to determine the status is a measurement of airflows, done with an anemometer on the air exhaust and air intake diffusers. Most often a building is under-pressurized, which means that the building sucks in radon gas from soil air beneath the building through the leaking spots in addition to fresh outside air through its ventilation intake diffusers.
It may also be of interest to measure the radon concentration in the soil air beneath the floor of the building. This can be done by drilling a hole through the floor of about 8–10 mm size (the diameter depends on the probe, used) and measure the radon gas with an integrated radon measuring instrument. It is also an effective way to check the types of material underneath the building with an endoscope. This will also allow for the radon professional to determine whether the soil permeability is suitable for including a subfloor suction system in the mitigation solution.
Once the radon professional has enough data to compare the measured radon value in the building with the radon level in the ground under the building, together with the ventilation data, it will be possible to calculate how much soil air is entering the building from the ground every hour by using Eq. (3) (see Ref. [14]):
𝐶 = ( )∗ ∗ 𝐶 ∗ 𝐿 (3)
where
𝐶 = Measured radon concentration in the house (Bq/m3)
𝐶 = Measured radon concentration in the ground under the building (Bq/m3) 𝜆 = Radon decay constant
V = Volume of air in the house (m3) n = Air exchange rate (air exchange/h)
L = Volume of soil air entering the building per hour (m3/h)
Two examples are provided to demonstrate the use of the equation to determine the volume of soil gas entering a house.
Example 1:
Assume the following parameters for the building:
Measured radon concentration in the house (Chouse) 500 Bq/m3
Air volume of a house (V) 500 m3
Air exchange rate ACH (n) 0.5/h
Measured radon concentration in soil under the building (Csoil) 2 000 Bq/m3
Radon decay constant 𝜆 0.00755
The volume of soil air (L) entering the building per hour can be estimated by application of Eq. (4) (see Ref. [14]):
𝐿 = (𝐶 ∙ (𝜆 + 𝑛) ∙ 𝑉) 𝐶⁄ (4)
For the example, the calculated volume of soil air entering the building is L = (500 * (0.00755 + 0.5) * 500) / 2 000 = 63.4 m3/h
Once the soil air volume entering the building is known, one can start searching for entry points and understand what to do about the identified problem. In example 1, where 63.4 m3/h of soil air enters the building, which is a lot of air, one can identify one major entry point is causing this large amount of soil air to entry to the building. That entry point can be, for example, an unsealed door to a crawl space or cellar.
In practice it is often lower airflow rates combined with higher radon concentrations in soil gas which are found entering a building, rather than those, demonstrated in example 1.
Example 2:
All parameter values are the same as in example 1, except for Csoil: Csoil = 40 000 Bq/m3.
In this case, the calculated volume of soil air entering the building is:
L = (500 * (0.00755 + 0.5) * 500) / 40 000 = 3.2 m3/h
This calculation demonstrates that, for a given concentration inside the building, the higher the concentration of radon in soil, the lower the flow rate of air into the building, and less obvious leakage spots can be expected. The challenge of mitigation in example 2 is to find the leakage spot or spots where a flow of only 3.2 m3/h enters the building. This is a very small amount of airflow, but due to the very high activity concentration of radon in the soil gas, it results in an activity concentration of 500 Bq/m3 of radon in indoor air of the building.
Thermography
A thermographic camera can be a very useful tool in investigating leakage spots for ingress of radon into a building, especially in colder climate countries. The camera image shows the spots where cold ground air is entering the construction instantly and gives the radon professional a hint on where to perform the radon “sniffing”. This saves time and allows to avoid an unnecessary use of the radon instruments.
Blower door test equipment
This equipment can be used to establish the airtightness of a building. The test involves fitting a temporary fan and frame into the entrance door to the building, and either blowing air into (pressurizing) or drawing air out of (depressurizing) the closed building. In addition to calculating the airtightness of the building, by using tracer smoke when running the fan, the professional can visually see smoke passing through gaps in the structure. This gives an indication of the soil air entry points.
3.2. RADON MITIGATION SOLUTIONS 3.2.1. Depressurization of the soil
The basic principle employed in depressurization of the soil is to ensure that the pressure difference between the soil and the building is always negative. Specifically, the absolute pressure in the soil is lower than the absolute pressure in the building at all surfaces adjacent to the soil and also at all points where radon gas could enter the inside of the building (e.g. floor sinks, piping penetrations, cracks).
In general, the depressurization of the soil approach is deemed to be most robust and successful compared to other approaches. However, soil depressurization might increase heat losses from the building. Nonetheless, with proper system design (i.e. minimizing necessary airflow from the soil to the outside) this effect can be minor. Active soil depressurization also necessitates the use of a fan, consuming electrical power. With proper design, the consumed power can be kept well below 1 to 5 kWh/day2 depending of the size of the fan used. Although the approach to mitigation using soil depressurization could be done using either as active or passive system, only active system is addressed here. Passive depressurization is prone to many different factors affecting its effectiveness. Passive systems always have to be designed in such a way that adaptation to an active system is possible and simple. In that sense the active system can be seen as a passive system, upgraded with active soil ventilation (depressurization). Currently there is much less data on the effectiveness of passive systems.
Active soil depressurization (ASD)
Active soil depressurization consists of the following elements:
Permeable layer;
Suction point(s);
Exhaust;
Sealing;
Fan;
Operation and monitoring system.
A sufficiently permeable layer is needed to allow the pressure field extension3 and to allow the radon gas to flow from the point of higher pressure (soil) to the point of lower pressure (suction point). This layer could be a layer of permeable gravel, a layer of corrugated plastic, or a layer of air below an air-tight membrane. An understanding of the composition of the air permeable layer is an important input to the design of the configuration of the ASD system.
2 This electrical fan consumption value assumes good sub-slab/soil communication/pressure field extension.
3 Pressure field extension refers to the effective area with lower soil gas pressure (i.e. effective area that has been
One or more suction points may be needed. There are different techniques to collect radon (radon pit, drain tiles, sumps or air voids under a membrane) at the suction point. The section point is directly connected to the suction pipe, so that radon, collected from a certain area (size of pressure field extension) is drawn through the suction pipe to outside the building. The number of suction points necessary depends upon each individual building e.g. permeability of the layer, footprint area of the building. However, through careful planning and execution it is usually possible to reduce the number of suction points to a few or even only one. Experience in the UK has shown that a single suction point will typically have an influence over an area of 250 m2 and a radius of 9 m [20].
The ASD system may have several different configurations:
(a) Sub-slab depressurization (SSD);
(b) Drain-tile depressurization (DTD).
The basic approach of the SSD and DTD systems is to create negative pressure under the existing ground concrete slab(s). A schematic representation of these two systems is presented in Figs 10 and 11.
FIG. 10. Sub-slab depressurization system [21]. Copyright 2020 AARST.
FIG. 11. Drain-tile system [21]. Copyright 2020 AARST.
These two configurations of the ASD system contain similar elements which are described in more detail below.
In order to ensure correct functioning of the SSD system, a sufficiently permeable layer needs to be available beneath the slab-on-grade. Prior diagnostics in the building will define the size of the negative pressure extension. Ideally, if a continuous layer of clean gravel a few centimetres thick is found beneath the slab, and if the layer extends across the whole area intended to be mitigated with a single suction point, it can be assumed the layer is sufficiently permeable.
If the DTD system is used, the drain tile is placed in a trench that is filled with permeable material. The function of the permeable layer is ensured through the drain-tile in direct contact with the soil air. It can be assumed that the negative pressure field extends over the whole surface of drain-tiles.
In the SSD system, soil gas containing radon migrates along the pressure difference towards the point of lowest pressure induced by the SSD system i.e. the suction point. To enhance radon gas collection, suction pits are constructed beneath the slab at the suction point(s). Suction pits are essentially voids of sufficient volume. A minimum size of 0.01 m3 is necessary. However, larger pits are recommended, ranging from 0.03 m3 to 0.05 m3. These provide a larger wall area and enhance the effectiveness of radon-gas extraction.
Locating the suction pits along known preferential pathways is important. These pathways usually exist near utility tunnels and along footing lines. Regardless of where the suction pits are located, there needs to be a knowledge of localized air leaks (weaknesses) into the radon system. Any air leaks from the indoor air into the ADS need to be sealed. If the air leaks cannot be reasonably sealed, then the suction pits need to be relocated.
In the DTD system, there is no need for a special pit. The whole void of the drain-tile assumes the function of a pit.
The piping used in SSD and DTD systems need to be designed in a way that it does not introduce significant airflow resistance. A minimum diameter of 100 mm is recommended in the case of single-family houses and 150 mm in the case of larger buildings.
The material for piping is country dependent. PVC piping is commonly used. The piping has to be durable and impact resistant. The piping may be designed in a way that the material of the piping changes (e.g. PVC to iron).
The design of the piping needs to ensure a continuous downwards slope of approximately 1 cm fall per 1 m of length to prevent creating unintentional water traps in the piping system. If this is not possible appropriate methods for maintaining obstruction-less airflow through the piping need to be employed.
The openings around the SSD and DTD suction pipes need to be sealed in a durable and permanent manner. At the penetration point taking the suction pipe through the floor, the gap between the pipe and the floor structure needs to be sufficiently wide to permit the sealant to flow into the gap, but sufficiently narrow to enable efficient sealing. A gap width between 10 and 15 mm is recommended.
The sealing needs to be done using a durable sealant compatible with all materials it comes in contact (e.g. PVC, concrete, polyethylene)4. The sealant has to provide a durable, permanently elastic seal. If necessary, surfaces may need to be treated with primer, depending on selected sealant.
The surfaces need to be clean and sufficiently firm. The gap has to be first prefilled with backer rod or comparable material to ensure the correct shape of the seal. After the backer rod is inserted, the sealant is applied. After the sealant has cured, further work can be done on radon system piping.
The fan is intended to induce the pressure difference in the system. Issues that need to be considered in selection of the fan and positioning of the fan are described in the Appendix.
Examples of different pipe routes and location of exhaust fans and roof level exhaust for building with sub-slab depressurization are presented in Figs 12, 13, 14 and 15.
FIG. 12. Sub-slab depressurization with internal fan in ceiling and roof level exhaust.
FIG. 13. Sub-slab depressurization with fan external to building and roof level exhaust.
FIG. 14. Sub-slab depressurization with internal fan in ceiling and roof level exhaust from building with basement.
FIG. 15. Sub-slab depressurization with fan external to building and roof level exhaust from basement.
With smaller buildings, such as houses where there is a space around the building, it is possible to core drill through the foundation to form a suction point at the edge of the floor and connect it to a fan with a low level exhaust. The exhaust outlet has to be located where it will not be a nuisance. Whilst a measurement of the radon level at the outlet will be very high, within a few metres of the outlet the gas will be dispersed. A schematic drawing of such a system is presented in Fig. 16. A photograph of the exhaust outlet is presented in Fig. 17. This design may not be allowed in some countries. It is strongly advised to measure radon in the living areas adjacent to the exhaust location to determine if radon is re-entering the building.
FIG. 16. External sub-slab depressurization low level exhaust.
FIG. 17. Example of a low level exhaust [20].
The operation of the system needs to be monitored continuously via an audible or visual pressure device. The owner of the building and/or building maintenance company representative needs to be provided with drawings of the system and a written operational manual.
Sub membrane depressurization (SMD)
The basic approach of the SMD system is to create negative pressure under a membrane. This design is used in cases where there is either no slab on the ground or the upper layer of the ground is permeable to an extent that prevents effective pressure field extension. It is also used in mitigating radon in buildings with crawl spaces. A schematic diagram of a sub-membrane depressurization system is shown in Fig. 18.
